Project Summary Rare genetic disorders (RGDs) have provided a significant window into the genetic architecture of cognitive and behavioral variation. They have also posed questions about the relationship between idiopathic and syndromic forms of cognitive and behavioral disorders, and the role of genetic background in RGD expression. Further, most genetic studies to date have focused on populations of European ancestry, meaning little is known about RGD expression and variability in other populations. To address these gaps, we will leverage the ongoing NeuroDev South Africa collection to genetically and phenotypically characterize 1,000 children aged 2-17, ascertained for Autism Spectrum Disorders, Intellectual Disability/Global Developmental Delay, and Attention Deficit Hyperactive Disorder in Cape Town. The collection also includes 1,000 case parents and 1,000 unrelated, ancestry-matched controls. We will genetically characterize all 3,000 NeuroDev participants in order to identify and investigate an estimated 300 RGD cases in the NeuroDev sample. We propose to use medical record data to further characterize all NeuroDev cases which, in conjunction with the detailed phenotype data collected as part of the core collection activity, will create uncommon opportunities for the phenotypic comparison of RGD-based and idiopathic neuropsychiatric disorders (e.g. dimensional cognitive and behavioral data, brain imaging, audiology data). With the aggregated data, we will compare the phenotypic features of RGD-based and idiopathic neuropsychiatric disorders and highlight points of divergence, which will be useful for addressing heterogeneity in future research, as well as in eventual treatment trials. Lastly, we consider the role of genetic background in the variable expressivity of neuropsychiatrically-involved RGDs, in terms of both genome-wide genetic risk for behavioral disorders and ancestral variation. These analyses will address several critical questions about the biology and presentation of RGDs, as well as their relationship to cognitive and behavioral disorders. The wide sharing of these data will permit further investigation at the field- wide level.